Tensioned touch panel and method of making same

ABSTRACT

A tensioned touch panel includes a support structure having a substrate with a generally planer conductive surface disposed thereon and an insulating spacer generally about the periphery of the substrate. A pretensioned conductive member overlies the support structure. The spacer separates the conductive membrane and the conductive surface thereby to define an air gap therebetween. A conductive membrane is secured to the support structure under sufficient tension to inhibit slack from developing in the conductive membrane as a result of changes in environmental conditions. A method of assembling a tensioned touch panel is also provided.

FIELD OF THE INVENTION

The present invention relates generally to touch systems and inparticular to a tensioned touch panel and method of making the same

BACKGROUND OF THE INVENTION

Touch panels such as for example digitizers and analog resistive touchscreens that make use of one or more tensioned membranes, are known inthe art. Tensioned touch panels of this nature typically include aconductive membrane that is stretched tautly over and spaced from aconductive substrate. When a pointer is used to contact the tensionedmembrane with sufficient activation force, the tensioned membranedeflects and contacts the conductive substrate thereby to make anelectrical contact. Determining voltage changes induced by theelectrical contact allows the position of pointer contact on thetensioned touch panel to be determined.

In order for such tensioned touch panels to work effectively, thespacing between the tensioned membrane and the conductive substrate mustbe maintained so that the tensioned membrane only contacts theconductive substrate when a pointer contact is made on the tensionedmembrane.

As will be appreciated, over time the tensioned membrane may sagcreating slack in the tensioned membrane. Changes in environmentalconditions such as humidity and/or temperature may also cause thetensioned membrane to expand resulting in slack developing in thetensioned membrane. If the tensioned membrane sags or expands, the slackdeveloped in the tensioned membrane may result in undesirable contactbetween the tensioned membrane and the conductive substrate. Thisproblem becomes more severe as the size of the touch panel becomesgreater.

A number of techniques have been considered to avoid undesirable contactbetween the tensioned membrane and the conductive substrate. Forexample, electrically insulating spacer dots may be disposed between thetensioned membrane and the conductive substrate at spaced locations overthe active contact area of the touch panel to maintain the spacingbetween the tensioned membrane and the conductive substrate. U.S. Pat.No. 5,220,136 to Kent discloses a contact touchscreen including suchinsulating spacer dots.

Although the use of insulating spacer dots maintains separation betweenthe tensioned membrane and the conductive substrate, the use ofinsulating spacer dots is problematic. In order to maintain separationbetween the tensioned membrane and the conductive substrate over theactive contact area of the touch panel, the insulating spacer dots mustbe positioned at locations within the active contact area. Thus, theinsulating spacer dots interrupt the active contact area of the touchpanel. As a result, contacts with the tensioned membrane over insulatingspacer dots will not register as contacts since the tensioned membranecannot be brought into electrical contact with the conductive substrateat those contact points. Also, the use of insulating spacer dots toseparate the tensioned membrane and the conductive substrate isexpensive. It is also difficult to maintain an even spacing between thetensioned membrane and the conductive substrate over the active contactarea using insulating spacer dots.

U.S. Pat. No. 5,838,309 to Robsky et al. discloses a self-tensioningmembrane touch screen that avoids the need for insulating spacer dots.The touch screen includes a support structure having a base and asubstrate support on which a conductive surface is disposed. Aperipheral insulating rail surrounds the conductive surface. Aperipheral flexible wall extends upwardly from the base. A conductivemembrane is stretched over the conductive surface and is attached to theperipheral flexible wall. The insulating rail acts to space theconductive membrane from the conductive surface. To inhibit sagging andmaintain tension on the conductive membrane, during assembly of thetouch screen the conductive membrane is attached to the flexible wallwhen the flexible wall is in a pretensioned state. In the assembledcondition, the flexible wall is biased outwardly and downwardly. As aresult, tension is continuously applied to the conductive membrane bythe flexible wall thereby to inhibit sagging of the conductive membrane.

U.S. Pat. No. 6,664,950 to Blanchard discloses a resistive touch panelhaving a removable, tensioned top layer and a base plate. The touchpanel may be situated relative to a display screen such that an air gapexists between the base plate and the display screen. The top plateincludes a transparent, flexible substrate having a hard transparentcoating, one or more anti-reflective coatings and an anti-fingerprintcoating thereon. The underside of the substrate is spaced from the uppersurface of the base plate by an air gap. To prevent wrinkling of the topplate, a stiff frame is bonded to the anti-fingerprint coating. Thestiff frame maintains tension in the top plate despite temperaturechanges.

Although the above references show touch panels having mechanisms tomaintain tension in the conductive membrane, manufacturing and labourcosts are associated with these tensioning mechanisms. Accordingly,improvements in tensioned touch panels to maintain the spacing betweenthe tensioned membrane and the conductive substrate are desired.

It is therefore an object of the present invention to provide a noveltensioned touch panel and method of making the same.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided amethod of assembling a touch panel including a support structure and aconductive membrane. The support structure has a conductive surface anda peripheral insulating spacer about the conductive surface. Theconductive membrane overlies the support structure with the spacerseparating the conductive membrane and the conductive surface thereby todefine an air gap therebetween. During the method, the conductivemembrane is pretensioned and the tensioned conductive membrane issecured to the support structure.

The pretensioning in one embodiment is selected to compensate for boththe coefficients of thermal expansion and hydroscopic or hygroscopicexpansion of the conductive membrane over a variety of temperature andhumidity conditions. The stress level is selected to be below the yieldpoint of the conductive membrane and at a level below which theconductive membrane exhibits significant creep i.e. creep where thetension in the conductive membrane drops over time to a level resultingin an unacceptable decrease in activation force and/or unwanted contactbetween the conductive membrane and the conductive surface. Theconductive membrane is bonded to the support structure via an adhesivesuch as for example an ultraviolet curing or cyanoacrylate (CA)adhesive.

The support structure includes a generally planar surface on which theconductive surface is disposed. The spacer is generally continuous andoverlies the peripheral region of the planar surface thereby to surroundthe conductive surface. The conductive membrane may be adhered directlyto the spacer or pulled around the spacer and adhered to the supportstructure.

According to another aspect of the present invention there is provided atensioned touch panel comprising a support structure including asubstrate having a generally planar conductive surface disposed thereonand an insulating spacer generally about the periphery of the substrate.A pretensioned conductive membrane overlies the support structure. Thespacer separates the conductive membrane and the conductive surfacethereby to define an air gap therebetween. The conductive membrane issecured to the support structure under sufficient tension to inhibitslack from developing in the conductive membrane as a result of changesin environmental conditions.

According to yet another aspect of the present invention there isprovided a tensioned touch panel comprising a support structure having aconductive surface disposed thereon. A conductive membrane overlies theconductive surface in spaced apart relation. The conductive membrane ispermanently secured to the substrate while under tension.

The present invention provides advantages in that an overall uniformtension can be maintained in the conductive membrane while reducingmanufacturing and labour costs of the tensioned touch panel. As aresult, slack is inhibited from developing in the conductive membraneregardless of environmental conditions while maintaining activationforces at user acceptable levels.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described more fullywith reference to the accompanying drawings in which:

FIG. 1 is a side cross-sectional view of a tensioned touch panel;

FIG. 2 is an enlarged portion of FIG. 1;

FIG. 3 shows steps performed during assembly of the tensioned touchpanel of FIG. 1;

FIG. 4 is a graph showing the stress versus strain characteristics of asample length of a conductive membrane and the theoretical stress versusstrain characteristics of the conductive membrane film;

FIG. 5 is a graph showing the theoretical strain versus activation forcecharacteristics of the conductive membrane;

FIG. 6 is a graph showing the creep characteristics of the conductivemembrane;

FIG. 7 is a graph showing cyclical elongation versus timecharacteristics of the conductive membrane film when subjected toalternating tensions of 8500 psi and zero psi respectively;

FIG. 8 is a front plan view of the tensioned touch panel of FIG. 1 in aninteractive display system;

FIG. 9 is a side cross-sectional view of another embodiment of atensioned touch panel;

FIG. 10 is a side cross-sectional view of yet another embodiment of atensioned touch panel;

FIG. 11 is a side cross-sectional view of yet another embodiment of atensioned touch panel;

FIG. 12 is a side cross-sectional view of still yet another embodimentof a tensioned touch panel; and

FIG. 13 is a side cross-sectional view of still yet another embodimentof a tensioned touch panel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIGS. 1 and 2, a tensioned touch panel is shown and isgenerally identified by reference numeral 10. Touch panel 10 in thisembodiment is generally rectangular and includes a support structure 12.Support structure 12 comprises a substrate 14 having a major top surface16, a major bottom surface 18 and sides 20 bridging the top and bottomsurfaces. The substrate 14 is formed of a rigid stable material such asfor example aluminum or other suitable rigid material. A conductivecarbon resistive layer 22 is bonded to the top surface 16 of thesubstrate 14 via an adhesive. A peripheral insulating spacer rail 30 isdisposed on the top surface 16 of the substrate 14. The insulatingspacer rail 30 is formed of electrically insulating material such as forexample rigid polyvinyl chloride (RPVC), acrylonitrile butadiene styrene(ABS), acrylic, fiberglass reinforced plastic (FRP) or coated aluminumand is bonded to the substrate 14 via an adhesive.

A flexible, elastic conductive membrane 40 under tension overlies thesupport structure 12 and is secured to the insulating spacer rail 30 bya fast drying adhesive such as for example, ultraviolet curing orcyanoacrylate (CA) adhesive. The conductive membrane 40 is layered andincludes an upper flexible, low creep film 44 such as for examplepolyethylene terephthalate (PET) and a lower conductive carbon resistivelayer 46 bonded to the film 44 by adhesive. The conductive resistivelayer 46 overlies the film 44 in the region corresponding to the activearea of the tensioned touch panel 10. Thus, a peripheral region 44 a ofthe film is free of the conductive resistive layer 46 allowing the film44 to be adhered directly to the insulating spacer rail 30.

The tension applied to the conductive membrane 40 maintains separationbetween the conductive membrane 40 and the conductive resistive layer 22on the top surface 16 of the substrate to define an air gap 48. Inparticular, the tension applied to the conductive membrane 40 beforebeing bonded to the insulating spacer rail 30 is selected to ensure thatthe air gap 48 is maintained over a significant length of time and overa variety of environmental conditions without significantly increasingthe activation force required to bring the conductive resistive layers22 and 46 into electrical contact in response to a contact made on thetensioned touch panel 10. In this manner, slack does not develop in theconductive membrane 40 making the tensioned touch panel 10 robust.

The tensioned touch panel 10 operates in a manner similar toconventional touch panels. When a pointer is used to contact thetensioned conductive membrane 40 with sufficient activation force, theconductive resistive layer 46 is brought into contact with theconductive resistive layer 22 at the contact location. Voltage changesinduced by the electrical contact between the conductive resistivelayers 22 and 46 are sensed allowing the position of the pointer contactto be determined.

Turning to FIG. 3, the steps performed during assembly of the tensionedtouch panel 10 are illustrated. The conductive membrane 40 is initiallyplaced in an assembly fixture and is stretched in both its lengthwiseand widthwise directions to place the conductive membrane 40 undertension. During stretching of the conductive membrane 40, the conductivemembrane 40 is subjected to stress generally in the range of from about1000 to 1500 pounds per square inch (psi). It has been found that thispretensioning of the conductive membrane 40 is sufficient to ensureeffective operation of the tensioned touch panel 10 over a variety ofenvironmental conditions while maintaining the activation force requiredto bring the conductive resistive layers 22 and 46 into electricalcontact at user acceptable levels. With the conductive membrane 40 underthe desired amount of tension, adhesive is placed on the peripheralregion 44 a of the film 44 that is free of the conductive resistivelayer 46 in a pattern corresponding to the insulating spacer rail 30.Alternatively the adhesive may be placed on the insulating spacer rail30 or on both the peripheral region 44 a of the film 44 and theinsulating spacer rail 30. The support structure 12 is then brought intocontact with the tensioned conductive member 40 to enable a secure bondto be formed between the insulating spacer rail 30 and the tensionedconductive membrane 40. Once the adhesive cures, the conductive membrane40 is released from the assembly fixture. Excess length of conductivemembrane 40 extending beyond the insulating spacer rail 30 is removed.

As mentioned above, the tension applied to the conductive membrane 40 isselected to inhibit slack from developing in the conductive membrane byusing the conductive membrane 40 itself as the means of maintainingtension. The end result is a highly reliable, robust touch panel 10 thatcan be easily manufactured in a low cost manner. In particular, thetension applied to the conductive membrane 40 prior to attachment to theinsulating spacer rail 30 is selected to compensate for the coefficientof thermal expansion (CTE) and the coefficient of hydroscopic orhygroscopic expansion (CHE) of the conductive membrane 40 withoutexceeding the yield point of the conductive membrane 40 and whilemaintaining the activation force at user acceptable levels. Bytensioning the conductive membrane 40 in this manner, the conductivemembrane 40 remains wrinkle free throughout a wide range of temperatureand humidity conditions while ensuring that an adequate, but notexcessive, activation force is required to bring the conductiveresistive layers 22 and 46 into contact in response to a contact made onthe tensioned touch panel 10. The tension of the conductive membrane 40simply reduces or increases depending on the temperature and humidityconditions while remaining wrinkle free.

A number of tests were performed on the conductive membrane 40 to ensureits suitability. During testing, the effect of the conductive resistivelayer 46 on the film 44 was assumed to be negligible to the overallcharacteristics of the conductive membrane 40 since the conductiveresistive layer 46 and bonding adhesive are both very thin and pliableas compared to the film 44. It was also assumed that the conductivemembrane 40 behaves in a linear fashion with respect to CTE and CHE andthat the activation force is a linear function of tension applied to theconductive membrane 40. Creep of the conductive membrane 40 was notconsidered to be a critical factor at the level of tension applied tothe conducive membrane 40 during assembly of the touch panel 10. Theconductive membrane 40 was also assumed to behave the same in both thelengthwise and widthwise directions.

Table 1 below shows the amount of elongation of a sample length of theconductive membrane 40 for various stresses applied to the conductivemembrane sample. TABLE 1 Sample Cross sectional area of sample length0.14125 Inches{circumflex over ( )}2 41.375 Inches Force Sampleelongation (lbs) (inches) stress (psi) % elongation 0.0 0 0 0.00000 11.80.004 84 0.00967 16.0 0.008 113 0.01934 22.0 0.011 156 0.02659 32.40.016 229 0.03867 50.4 0.021 357 0.05076 73.0 0.033 517 0.07976 86.00.036 609 0.08701 100.8 0.045 714 0.10876 119.4 0.052 845 0.12568 136.00.06 963 0.14502 155.8 0.067 1103 0.16193 169.5 0.072 1200 0.17402 178.60.076 1264 0.18369 187.0 0.078 1324 0.18852 189.0 0.079 1338 0.19094199.0 0.086 1409 0.20785FIG. 4 is a graph showing the stress versus strain data of Table 1together with the theoretical stress versus strain characteristics ofthe film 44. As will be appreciated, the behaviour of the conductivemembrane 40 corresponds very well with the theoretical stress versusstrain data.

The relative change in dimension between the conductive membrane 40 andthe support structure 12 at a variety of environmental conditions werecalculated for a tensioned touch panel 10 having an active contact area60 inches in length and 48 inches in width. For the purpose of thesecalculation, the following assumptions were made: Conductive membraneCTE: 0.000017 in/in/° C. Conductive membrane CHE: 0.00006 in/in/% RHSupport structure CTE: 0.0000237 in/in/° C. Temperature during assembly:21° C. Humidity during assembly: 44%

Based on the above assumptions and looking at the longest dimension ofthe conductive membrane 40 where changes are greater than in the shorterdimension, the change in the size of the conductive membrane 40 for each1° C. increase in temperature above the assembly temperature can becalculated as follows:0.000017″/″/°*60″*1°=0.00102″

The change in size of the support structure 12 for each 1° C. increasein temperature above the assembly temperature can be calculated asfollows:0.0000237″/″/°*60″*1°=0.00142″

The change in size of the conductive membrane 40 for each 1% increase inrelative humidity (RH) above the assembly humidity can be calculated asfollows:0.000006″/″/%*60″*1%=0.00036″

The effects of the CTE and CHE are cumulative for the conductivemembrane 40, so for a 1° C. temperature increase and a 1% increase inrelative humidity, the net change in size of the conductive membrane 40is:0.00102″+0.00036″=0.00138″

The relative change in size between the conductive membrane 40 and thesupport structure 12 for a 1° C. temperature increase and a 1% increasein relative humidity above the assembly conditions is therefore:0.00138″−0.00142″=−0.00004″

The negative number indicates that the conductive membrane 40 grew lessthan the support structure 12. Since the conductive membrane 40 isrigidly and permanently bonded to the support structure 12, theconductive membrane 40 was stretched by the support structure 12 anamount equal to 0.00004″.

An interactive analysis of the effects of temperature and humidity wasperformed using the above calculations to allow the changes in size ofthe conductive membrane to be calculated over a variety of environmentalconditions differing from assembly conditions. For example, consider thefollowing assembly and in service conditions where the in serviceconditions represent a typical office environment:

-   Assembly conditions: 20° C.@40% RH-   In service conditions: 23° C.@60% RH    In these in service conditions, the size of the conductive membrane    40 would increase by 0.006″.

Consider more severe in service conditions that may represent a shippingenvironment:

-   Assembly conditions: 20° C.@35% RH-   In service conditions: 50° C.@95% RH    In these in service conditions, the size of the conductive membrane    40 would increase by 0.009″.

Consider opposite end extreme in service conditions that may alsorepresent a shipping environment:

-   Assembly conditions: 20° C.@35% RH-   In service conditions: −40° C.@15% RH    In these in service conditions, the size of the conductive membrane    would increase by 0.016″.

During assembly of the touch panel 10, the conductive membrane 40 isstretched by more than the above calculated amounts prior to beingattached to the insulating spacer rail 30 of the support structure 12.As a result, changes in environmental conditions causing the conductivemembrane 40 to expand do not create slack in the conductive membrane 40.Rather these environmental changes affect the tension, or stress in theconductive membrane 40 and therefore, simply alter the activation force.Since the activation force generated by a certain strain is known, theactivation force can be plotted as a line as shown in FIG. 5.

Line 60 in the graph of FIG. 5 shows the theoretical relationshipbetween strain of the conductive membrane 40 and the resultingactivation force. The intersection point of line 62 and line 60represents the activation force required to bring the conductiveresistive layers 22 and 46 into electrical contact at assemblyconditions of 21° C.@44% RH. The intersection point of line 64 and line60 represents the activation force required to bring the conductiveresistive layers 22 an 46 into electrical contact at environmentalconditions of 40° C.@85% RH. The difference along the x-axis between thetwo intersection points represents the resulting change in activationforce. In the above example, there is a decrease in activation forceequal to about 6 or 7 grams.

Creep of the conductive membrane 40 after assembly of the touch panel 10is also of concern. If the conductive membrane 40 were to creepsignificantly after assembly of the touch panel 10, the activation forcewould drop gradually as the internal stress of the conductive membrane40 relaxed. Creep data for the film 44 is shown in FIG. 6. The graphdepicts creep as the change in elongation over time at a fixed stress.The flatter the line, the less creep exhibited by the film 44. As can beseen, creep is very low at the tension used to pretension conductivemembrane 40 during assembly. The line is very flat at stresses in the1000 to 1500 psi range.

The effect of cyclical, or alternating stresses is also of concern inthat the touch panel 10 may encounter many changes in environmentalconditions during shipping. FIG. 7 shows data for the film 44 when thefilm is subjected to alternating tensions of 8500 psi and zero psirespectively. As can be seen, the film 44 exhibits a slight creep underthese conditions as the bottom of each cycle is slightly higher than theprevious cycle. Since the strain applied to the conductive membrane 40during assembly of the touch panel 10 and over a variety ofenvironmental conditions is significantly less than 8500 psi, it isbelieved that the effect of cyclical, or alternating stresses will benegligile.

FIG. 8 shows the tensioned touch panel 10 in an interactive touch system100 of the type disclosed in U.S. Pat. No. 5,448,263 to Martin, thecontent of which is incorporated herein by reference. As can be seen,the tensioned touch panel 10 is coupled to a computer 102. Computer 102provides image data to a projector 104 which in turn projects an image106 on the touch panel 10. Sensed pointer contacts on the touch panel 10that are sufficient to bring the conductive resistive layers 22 and 46into electrical contact are conveyed to the computer 102, which in turnupdates the image data conveyed to the projector 104 so that the image106 projected on the touch panel 10 reflects pointer contacts. The touchpanel 10, computer 102 and projector 104 thus form a closed loop.Alternatively, the tensioned touch panel 10 may be used in conjunctionwith a rear projection system.

FIG. 9 shows another embodiment of a tensioned touch panel 110 similarto that of FIG. 1. In this embodiment, the conductive resistive layer146 adhered to the film 144 overlies the entire surface of the film 144that faces the support structure 12 thereby eliminating the peripheralmargin 44 a.

FIG. 10 shows yet another embodiment of a tensioned touch panel 210. Inthis embodiment, the insulating spacer rail 230 is generally L-shaped insection. One arm 230 a of the insulating spacer rail 230 overlies theperiphery of the top surface 216 of the substrate 214. The other arm 230b of the insulating spacer rail 230 abuts the sides 220 of the substrate214.

FIG. 11 shows yet another embodiment of a tensioned touch panel 310. Inthis embodiment the insulating spacer rail 330 is C-shaped in sectionand completely surrounds the sides 320 of the substrate 314. The upperarm 330 a of the insulating spacer rail 330 overlies the periphery ofthe top surface 316 of the substrate 314. The lower arm 330 b of theinsulating spacer rail 330 overlies the periphery of the bottom surface318 of the substrate 314. The bight 330 c of the insulating spacer rail330 abuts the sides 320 of the substrate 314. The conductive membrane340 is similar to that shown in FIG. 1 and is bonded to the top surfaceof the upper arm 330 a.

FIGS. 12 and 13 show still yet further embodiments of tensioned touchpanels 410 and 510 respectively similar to that of FIG. 11. In FIG. 12,the conductive membrane 440 overlies the entire outer surface of theinsulating spacer rail 430 and is bonded to the upper and lower arms 430a and 430 b as well as the bight 430 c of the insulating spacer rail430. In the embodiment of FIG. 13, the conductive membrane 540 alsooverlies the entire outer surface of the insulating spacer rail 530 butextends beyond the lower arm 530 b of the insulating spacer rail 530 andis bonded to the bottom surface 518 of the substrate 514.

Although the conductive membranes illustrated in FIGS. 10 to 13 show theconductive resistive layer covering the entire surface of the film thatfaces the support structure, conductive membranes of the form shown inFIG. 1 can of course be used.

Although a number of embodiments of the tensioned touch panel have beendescribed and illustrated, those of skill in the art will appreciatethat other variations and modifications may be made without departingfrom the spirit and scope thereof as defined by the appended claims. Forexample, the support structure need not be rectangular. The presentmethod allows tensioned touch panels of virtually any shape to beconstructed. Ultraviolet and CA adhesives were selected to secure theconductive membrane to the support structure due to their fast curetimes. Other suitable adhesives can of course also be used. Theperipheral insulating spacer rails need not to be adhered to the supportstructure. Other suitable fastening means may of course be used tosecure the insulating spacer rails to the support structure.

1. A method of assembling a touch panel including a support structureand a conductive membrane, said support structure having a conductivesurface and a peripheral insulating spacer about said conductivesurface, said conductive membrane overlying said support structure withsaid spacer separating said conductive membrane and said conductivesurface thereby to define an air gap therebetween, said methodcomprising: pretensioning the conductive membrane; and securing thetensioned conductive membrane to the support structure.
 2. The method ofclaim 1 wherein said pretensioning is selected to compensate for atleast one of the coefficient of thermal expansion and the coefficient ofhydroscopic or hygroscopic expansion of said conductive membrane over avariety of environmental conditions.
 3. The method of claim 2 whereinsaid pretensioning is selected to compensate for both the coefficientsof thermal expansion and hydroscopic or hygroscopic expansion of saidconductive membrane over a variety of temperature and humidityconditions.
 4. The method of claim 3 wherein said conductive membrane isbonded to said support structure via an adhesive.
 5. The method of claim4 wherein said adhesive is an ultraviolet curing adhesive.
 6. The methodof claim 4 wherein said adhesive is a cyanoacrylate adhesive.
 7. Themethod of claim 3 wherein said conductive membrane is adhered to saidspacer.
 8. The method of claim 7 wherein said adhesive is an ultravioletcuring adhesive.
 9. The method of claim 7 wherein said adhesive is acyanoacrylate adhesive.
 10. The method of claim 3 wherein said supportstructure includes a substrate having a generally planar surface onwhich said conductive surface is disposed and wherein said spacer isgenerally continuous and overlies the peripheral region of said planarsurface thereby to surround said conductive surface.
 11. The method ofclaim 10 wherein said spacer is a rail overlying said peripheral regionand wherein said conductive membrane is adhered directly to said rail.12. The method of claim 10 wherein said spacer is a rail about theperiphery of said substrate, said rail being generally L-shaped in sidesection and including one arm portion disposed on the peripheral regionof said planar surface and another arm portion abutting the sides ofsaid substrate, said conductive membrane being adhered directly to saidrail.
 13. The method of claim 10 wherein said spacer is a rail about theperiphery of said substrate, said rail being generally C-shaped in sidesection and including one arm portion disposed on the peripheral regionof said planar surface, another arm portion disposed on an opposedsurface of said substrate and a bight joining said arm portions andabutting the sides of said substrate, said conductive membrane beingadhered to at least one of said rail and opposed surface.
 14. The methodof claim 13 wherein said conductive membrane is adhered to said rail.15. The method of claim 13 wherein said conductive membrane is adheredto said opposed surface.
 16. The method of claim 3 wherein during saidpretensioning, said conductive membrane is subjected to stress at alevel below the yield point of said conductive membrane and below alevel at which said conductive membrane exhibits significant creep. 17.The method of claim 16 wherein during said pretensioning, saidconductive membrane is subjected to stress in the range of from about1000 to 1500 psi.
 18. A tensioned touch panel comprising: a supportstructure including a substrate having a generally planar conductivesurface disposed thereon and an insulating spacer generally about theperiphery of said substrate; and a pretensioned conductive membraneoverlying said support structure, said spacer separating said conductivemembrane and said conductive surface thereby to define an air gaptherebetween, said conductive membrane being secured to said supportstructure under sufficient tension to inhibit slack from developing insaid conductive membrane as a result of changes in environmentalconditions.
 19. A tensioned touch panel according to claim 18 whereinsaid conductive membrane is subjected to stress at a level selected tocompensate for the coefficient of thermal and hydroscopic or hygroscopicexpansion of said conductive membrane over a variety of temperature andhumidity conditions prior to being secured to said support structure.20. A tensioned touch panel according to claim 19 wherein said stresslevel is below the yield point of said conductive membrane and below alevel at which said conductive membrane exhibits significant creep. 21.A tensioned touch panel according to claim 20 wherein said stress levelis in the range of from about 1000 to 1500 psi.
 22. A tensioned touchpanel according to claim 20 wherein said conductive membrane is adheredto said support structure.
 23. A tensioned touch panel according toclaim 22 wherein said adhesive is an ultraviolet curing adhesive.
 24. Atensioned touch panel according to claim 22 wherein said adhesive is acyanoacrylate adhesive.
 25. A tensioned touch panel according to claim22 wherein said spacer is a generally continuous rail about theperiphery of said substrate.
 26. A tensioned touch panel according toclaim 25 wherein said rail overlies a peripheral region of saidsubstrate surrounding said conductive surface, said conductive membranebeing adhered directly to said rail.
 27. A tensioned touch panelaccording to claim 25 wherein said rail is generally L-shaped in sidesection and includes one arm portion overlying said peripheral regionand another arm portion abutting the sides of said substrate, saidconductive member being adhered directly to said rail.
 28. A tensionedtouch panel according to claim 25 wherein said rail is generallyC-shaped in side section and includes one arm portion overlying saidperipheral region, another arm portion overlying an opposed surface ofsaid substrate and a bight joining said arm portions and abutting thesides of said substrate, said conductive member being adhered to atleast one of said rail and opposed surface.
 29. A tensioned touch panelaccording to claim 28 wherein said conductive membrane is adhered tosaid rail.
 30. A tensioned touch panel according to claim 28 whereinsaid conductive membrane is adhered to said opposed surface.
 31. Atensioned touch panel according to claim 20 wherein said conductivemembrane includes a film and a conductive layer on said film, saidconductive layer facing said conductive surface.
 32. A tensioned touchpanel according to claim 31 wherein said conductive layer covers aportion of a major surface of said film defining a peripheral margin,said peripheral margin corresponding generally in shape to said spacer.33. A tensioned touch panel according to claim 31 wherein saidconductive layer covers the entirety of a major surface of said film.34. A tensioned touch panel comprising: a support structure having aconductive surface disposed thereon; and a conductive membrane overlyingsaid conductive surface in spaced apart relation, said conductivemembrane being permanently secured to said substrate while undertension.
 35. A tensioned touch panel according to claim 34 wherein saidconductive membrane is adhered to said support structure.
 36. Atensioned touch panel according to claim 35 wherein said adhesive is anultraviolet curing adhesive.
 37. A tensioned touch panel according toclaim 35 wherein said adhesive is a cyanoacrylate adhesive.
 38. Atensioned touch panel according to claim 35 wherein said conductivemembrane is subjected to stress at a level selected to compensate forthe coefficient of thermal and hydroscopic or hygroscopic expansion ofsaid conductive membrane over a variety of temperature and humidityconditions.
 39. A tensioned touch panel according to claim 38 whereinsaid stress level is below the yield point of said conductive membraneand below a level at which said conductive membrane exhibits significantcreep.
 40. A tensioned touch panel according to claim 39 wherein saidstress level is in the range of from about 1000 to 1500 psi.